Acidity, Accessibility, and Stability of Hydroxyl Groups in Y-Zeolites

65

Acidity,

Accessibility,

and

Stability

of

Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on December 9, 2014 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0102.ch065

Hydroxyl Groups in Y-Zeolites L. MOSCOU Koninklijke Zwavelzuurfabrieken v/h Ketjen N.V., P.O. Box 15-C, Amsterdam, The Netherlands

Determination of acidic OH groups in Y-zeolites by LiAlH reaction and Karl Fischer titration indicates that after heat ing to 200°-300°C, REY zeolite contains only OH groups in α-cages equivalent to one OH for each rare earth ion in troduced. Further heating causes dehydroxylation, which is accompanied by a new formation of Bronsted sites in α-cages, up to a maximum of half the amount present at 250°C. In NH Y zeolite, deammoniation causes OH group formation in both a- and β-cages. Fully exchanged N H Y zeolite contains 10 OH groups in α-cages per gram of zeo lite. HY zeolite behavior compares well with the NH Y zeolite properties. The data support the assumption that OH groups with 3640 cm infrared frequency are the acces sible OH groups in a-cages. 4

4

4

21

4

-1

/ C a t a l y t i c properties o f c r y s t a l l i n e a l u m i n o s i l i c a t e s g e n e r a l l y are c o r r e ^

l a t e d w i t h a c i d i c species i n t h e zeolite f r a m e w o r k .

M a n y reports

d e a l w i t h t h e n a t u r e a n d l o c a t i o n of this a c i d i t y , w h i c h has b e e n exten s i v e l y i n v e s t i g a t e d w i t h i n f r a r e d spectroscopy b e f o r e a n d after r e a c t i o n of t h e zeolite w i t h b a s i c species. T h e l i m i t a t i o n of i n f r a r e d studies o n zeolites is t h e strong a d s o r p t i o n o f w a t e r , g i v i n g rise to b r o a d o v e r l a p p i n g b a n d s i n t h e i n f r a r e d s p e c t r u m . F o r this reason, o n l y those zeolites c a n b e s t u d i e d w h i c h are h i g h l y d e h y d r a t e d , either b y h e a t i n g to 200 ° C a n d a b o v e or b y e v a c u a t i o n . Prior work (3) techniques—loss

has i n d i c a t e d that a c o m b i n a t i o n of 3 a n a l y t i c a l

of w e i g h t o n i g n i t i o n ( L O I ) , K a r l F i s c h e r t i t r a t i o n

( K F ) , a n d reaction w i t h L i A l H — r e s u l t s i n quantitative data o n the 4

a m o u n t of a c i d i c O H groups i n the zeolite, e v e n i n n o n h e a t e d w e t s a m ples.

This method discriminates between

acidic a n d non-acidic O H

337

In Molecular Sieve Zeolites-II; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1971.

338

MOLECULAR

Table I.

SIEVE

ZEOLITES

Measurement of Water and H y d r o x y l Groups in Y-Zeolites Measured Group

Position

LOI

KF

H 0 H 0 H 0 Acidic O H Nonacidic O H Acidic + nonacidic O H

Between crystallites α-Cages β-Cages α-Cages α-Cages β-Cages

X X X X X X

X X

2

2

2


Π

Table II.

N a Y zeolite sample R E Y zeolite sample R E Y zeolite sample R E Y zeolite sample N H Y zeolite s a m p l e N H Y zeolite sample H Y zeolite sample 4

LiAlH

4

X X X

Chemical Analysis of Zeolites ( D r y Basis) %

4

With

Να,Ο 13.7 3.53 5.90 9.1 5.95 0.54 5.90

A Β C D Ε F G

%

REzOz

%ΝΗ;

16.1 12.9 7.2 4.02 7.7

g r o u p s a n d also b e t w e e n g r o u p s present i n the supercages

(α-cages)

of

the c r y s t a l a n d groups present i n sodalite cages ( β - c a g e s ) a n d h e x a g o n a l prisms. T h e present p a p e r deals w i t h the a p p l i c a t i o n of these t e c h n i q u e s to s t u d y the f o r m a t i o n , a c c e s s i b i l i t y , a n d s t a b i l i t y o f a c i d i c h y d r o x y l g r o u p s i n Y - t y p e zeolites. C o m p a r i s o n is m a d e b e t w e e n N a Y , R E Y , N H Y , a n d 4

H Y zeolites. Experimental T h e analytical techniques p a p e r (3).

u s e d are d e s c r i b e d f u l l y i n the

earlier

A s u m m a r y is g i v e n i n T a b l e I, s h o w i n g t h e v a r i o u s m e t h o d s

a n d the groups d e t e r m i n e d b y t h e m . T h e L O I is d e f i n e d as t h e w e i g h t loss of the heat-treated s a m p l e o n its subsequent c a l c i n a t i o n at 1000 ° C for 1 h r . T h u s , it gives the s u m of r e s i d u a l w a t e r a n d O H g r o u p s w h i c h c a n b e d e h y d r o x y l a t e d at 1 0 0 0 ° C . F o r N H - c o n t a i n i n g zeolites, the L O I is c o r r e c t e d f o r the w e i g h t of 4

NH

3

i n the s a m p l e .

T h e K F t i t r a t i o n m e t h o d is b a s e d o n t h e r e a c t i o n

of w a t e r w i t h i o d i n e a n d S 0 ; a possible s l o w r e a c t i o n of h y d r o x y l groups 2

w i t h the reagent is e x c l u d e d b y e x t r a p o l a t i n g the t i t r a t i o n c u r v e to zero t i m e , w i t h constant excess of reagent (4).

T h e analysis w i t h L i A l H

4

is

b a s e d o n its r e a c t i o n w i t h w a t e r a n d a c i d i c h y d r o x y l groups, b o t h u n d e r e v o l u t i o n of h y d r o g e n gas.


65.

Moscou

Hydroxyl

Groups in

Acidity of H y d r o x y l Groups.

339

Ύ-Zeolites

T a b l e I shows that t h e a m o u n t of

a c i d i c O H g r o u p s ( B r o n s t e d sites, O H ) i n α-cages is o b t a i n e d b y t a k i n g +

the difference b e t w e e n L i A l H

4

a n d K F titrations. E a r l i e r w o r k i n d i c a t e d

that e v e n w e a k l y a c i d i c s i l a n o l g r o u p s i n a m o r p h o u s s i l i c a react q u a n titatively w i t h L i A l H ^

(I).

4

E a c h hydrogen i o n w i t h a n a c i d strength

s i l a n o l a c i d i t y is e x p e c t e d t o react w i t h t h e reagent.

Basic hydroxyl


g r o u p s l i k e those present i n rare e a r t h h y d r o x y d e s are i n e r t to L1AIH4. Accessibility of Acidic H y d r o x y l Groups.

T h e difference

between

L1AIH4 a n d K F t i t r a t i o n d a t a gives the a c i d i c O H content i n α-cages o n l y because n e i t h e r t h e L1AIH4 n o r t h e i o d i n e m o l e c u l e c a n enter t h e β-cage. Stability of Acidic H y d r o x y l Groups.

T h e s t a b i l i t y of a c i d i c O H

g r o u p s is i n v e s t i g a t e d b y t i t r a t i n g zeolites after v a r i o u s heat treatments. C a r e w a s t a k e n that d u r i n g h a n d l i n g of t h e heat-treated

zeolite o n l y

n e g l i g i b l e a m o u n t s of w a t e r c o u l d b e r e a d s o r b e d . Zeolite Preparation.

N a Y zeolite, o b t a i n e d f r o m U n i o n C a r b i d e ,

L i n d e D i v i s i o n , w a s p u r i f i e d f r o m free s o d i u m silicate b y r e p e a t e d w a s h i n g w i t h w a t e r u n t i l t h e m o l a r r a t i o of t h e zeolite w a s N a 0 : A l 0 : S i 0 2

=

1.03:1.00:4.90.

2

3

2

T h e R E Y zeolites w e r e o b t a i n e d f r o m t h e p u r i f i e d

N a Y z e o l i t e b y exchange of s o d i u m ions w i t h rare earth ions i n R E C 1

3

s o l u t i o n . N H Y zeolites w e r e o b t a i n e d b y t r e a t i n g the p u r i f i e d N a Y zeo 4

lite w i t h NH4CI s o l u t i o n ( 5 0 % e x c h a n g e ) .

M o r e exchange steps w e r e

n e e d e d t o r e m o v e 9 5 % o f t h e N a ions. H Y z e o l i t e w a s o b t a i n e d f r o m +

the p u r i f i e d N a Y z e o l i t e b y t r e a t i n g a z e o l i t e - w a t e r suspension w i t h a w e a k l y a c i d i c i o n - e x c h a n g e r e s i n i n the p r o t o n f o r m at 2 0 ° C (2).

Table

I I shows t h e c h e m i c a l c o m p o s i t i o n of the zeolites o b t a i n e d . A l l zeolites w e r e h i g h l y c r y s t a l l i n e i n x-ray analysis. Results A n a l y s i s d a t a of 4 samples of zeolites are s u m m a r i z e d i n T a b l e I I I , w h e r e N a Y , R E Y , N H Y , a n d H Y zeolites are c o m p a r e d . F o r e a c h zeo 4

lite, 3 sets of d a t a are g i v e n : t h e loss o n i g n i t i o n , t h e difference b e t w e e n LOI

a n d L1AIH4 =

H

2

0 - f O H i n β-cages

α - c a g e s ) , a n d t h e difference b e t w e e n L i A l H α-cages.

4

( a n d nonacidic O H i n and K F =

acidic O H i n

N o n a c i d i c O H i n α-cages c a n n o t b e d i s t i n g u i s h e d separately

a n d h e n c e are n o t d i s c u s s e d f u r t h e r .

H e a t p r e t r e a t m e n t o f zeolites w a s

c a r r i e d o u t i n 2 w a y s — i . e . , h e a t i n g f o r a f e w h o u r s at a constant

tem

p e r a t u r e a n d h e a t i n g at a constant rate of 1 0 ° C / m i n u n t i l a g i v e n t e m p e r ature is r e a c h e d . X - r a y d i f f r a c t i o n analysis o f t h e v a r i o u s heat-treated

samples i n

dicates that f r a m e w o r k collapse occurs a b o v e the f o l l o w i n g

tempera

tures: N a Y , 8 0 0 ° C ; R E Y , 9 0 0 ° C ; N H Y , 8 0 0 ° C ; H Y , 8 0 0 ° C .

T h e data

4

i n T a b l e I I I s h o w that i n N a Y z e o l i t e n o a c i d i c O H g r o u p s are present


340

MOLECULAR

Table III. NaY,


Pretreatment Temp., °C At At Till Till Till Till Till Till Till Till Till Till a

LOI

H0 2

Sample A +

OH

(»

120 160 200 250 300 350 400 500 600 700 800 900

SIEVE

LOI

(«)

7.9 10.3

3.4 2.9

0.0 0.0

4.1

2.1

0.0

2.0 1.6 1.3 1.0

1.1 1.1 0.9 0.6

0.0 0.1 0.0 0.0

II

A n a l y s i s o f Zeolites, REY,

0H+

ZEOLITES

H0 2

Sample

Β

+ OH (β)

0H+

(«)

15.3 8.0 19.4

5.8 3.9 4.2

0.0 1.0 0.0

4.8 4.5 2.9 2.4 1.9 1.6 1.4 0.6

2.5 3.4 1.8 1.7 1.3 1.1 1.1 0.4

0.9 0.3 0.5 0.5 0.5 0.4 0.1 0.0

All data in % H 0 d.b. 2

i n «-cages.

T h e m a x i m a l a c i d i c O H - a content f o u n d f o r t h e 3 R E Y

zeolites u n d e r i n v e s t i g a t i o n is g i v e n i n T a b l e I V , c o m p a r i n g t h e e x p e r i m e n t a l l y f o u n d values w i t h t h e values c a l c u l a t e d f r o m t h e R E content of t h e z e o l i t e , a s s u m i n g that e a c h R E i o n gives o n e a c i d i c O H g r o u p ( 5 ) . T a b l e I V i n d i c a t e s that e a c h rare e a r t h i o n i n t h e zeolite forms a p p r o x i m a t e l y one a c i d i c h y d r o x y l g r o u p i n α-cages. In

F i g u r e 1, t h e difference b e t w e e n

L O I and L i A l H

4

is p l o t t e d

against t h e L O I f o r t h e 4 types o f zeolites u n d e r i n v e s t i g a t i o n . I t shows that t h e curves f o r t h e R E Y a n d N a Y zeolites a b o v e 4 . 5 % L O I are n e a r l y i d e n t i c a l . A t l o w e r L O I v a l u e s , the R E Y c u r v e is i d e n t i c a l to t h e N H Y 4

a n d H Y curves. T h e t h e r m a l s t a b i l i t y of a c i d i c O H groups i n α-cages is s h o w n i n F i g u r e 2. T h e c u r v e f o r R E Y zeolite shows 2 characteristics—viz.,

a sig

n i f i c a n t m i n i m u m i n t h e c u r v e at temperatures b e t w e e n 3 5 0 ° a n d 500 ° C , a n d t h e h e i g h t of t h e s e c o n d p a r t of t h e c u r v e is h a l f that of t h e first p a r t of t h e c u r v e . these

A l l 3 R E Y zeolite samples

( B , C , and D ) showed

characteristics.

T h e results f r o m t h e N H Y 4

a n d H Y zeolite analysis are g i v e n i n

T a b l e s I I I a n d V a n d i n F i g u r e s 1 a n d 2. F i g u r e 1 indicates that f o r b o t h N H Y a n d H Y zeolites, t h e content 4

of w a t e r a n d O H g r o u p s i n β-cages is s i g n i f i c a n t l y h i g h e r t h a n f o r N a Y a n d R E Y zeolites, w h i c h indicates that i n contrast to N a Y a n d R E Y , t h e N H Y a n d H Y zeolites d o c o n t a i n O H groups i n t h e β-cages. 4

T h i s agrees

w e l l w i t h t h e d a t a i n T a b l e s I I I a n d V , s h o w i n g that N H Y s a m p l e Ε 4

exposes a m a x i m u m of a c i d i c O H groups i n α-cages after a 250 ° C treat-


65.

Moscou

Hydroxyl

Groups in

341

Y-Zeolites

Dried at Different Temperatures NH Y, 4


LOI

H0 2

10.4 15.8 6.0

Sample + OH (β) 5.2 5.9 3.9

3.9 3.6 2.8 1.9 1.6

2.8 2.4 1.9 1.3 1.0

Table I V .

Ε

HY, Sample

OH+

LOI

H0 2

(«) 0.8 0.0 1.1

0.6 0.6 0.4 0.1 0.2

+

(»

OH

G OH+ («)

11.8 21.9

7.9 6.4

0.0 0.0

6.4

5.1

0.4

3.6 3.4 1.6 1.3 1.3

2.5 2.6 0.9 0.7 0.8

0.7 0.6 0.4 0.4 0.2

Comparison of Measured and Calculated O H (a) Densities in R E - Y Zeolites Measured

Sample R E Y sample Β R E Y sample C R E Y sample D

Max. OH (a) content, %H 0 2

1.04 0.82 0.58

Calculated

Number of OH (a) per gram zeolite 6.9 Χ 1 0 5.5 Χ 1 0 3.9 Χ 1 0

20 20 20

%

RE O in zeolite 2

16.1 12.9 7.2

z

Number of (λ per gram zeolite 6.4 Χ 1 0 5.2 Χ 1 0 2.9 Χ 1 0

20 20 20

Figure 1. Relation between the difference of LOI and LiAlHt (H 0 + OH in β-cages and nonacidic OH in α-cages) and foss on ignition for Y-type zeolites 2


342

MOLECULAR SIEVE ZEOLITES II

Acidic 1 2 , OH in o c c a g e s ( % H 0 ) 2


RE-Y HY 2 0 0 4 0 0 6 0 0 8 0 01 0 0 0 >P r e t r e a t m e n t t e m p (°C) Figure 2.

Thermal stability

of acidic OH groups in α-cages zeolites

of

Y-type

m e n t w h i c h is exactly h a l f the a m o u n t of O H g r o u p s , as c a l c u l a t e d f r o m the N H

content of the zeolite.

4

F o r the H Y zeolite, 1/3

a m o u n t of O H g r o u p s is present i n α-cages.

of the t o t a l

T h e temperature

regions

w h e r e f o r m a t i o n a n d d e h y d r o x y l a t i o n of O H g r o u p s i n α-cages of H Y a n d N H Y zeolites o c c u r are clear f r o m F i g u r e 2. 4

Discussion I n N a Y zeolite, no a c i d i c h y d r o x y l groups are f o u n d i n α-cages;

the

presence of O H groups i n β-cages c a n n o t b e d e t e r m i n e d q u a n t i t a t i v e l y , b u t seems v e r y u n l i k e l y f r o m i n f r a r e d studies

(10).

T h e m a x i m u m i n the a c i d i c O H content i n α-cages of R E Y zeolites is present after h e a t i n g the z e o l i t e to 2 0 0 ° - 3 0 0 ° C

(Figure 2), while under

these c o n d i t i o n s O H groups i n β-cages are p r o b a b l y absent, as c a n be i n f e r r e d f r o m the i d e n t i t y of the N a Y a n d R E Y curves i n F i g u r e 1. absolute

q u a n t i t y of O H ( a ) Table V .

groups is i n g o o d agreement w i t h

Max. OH (a) content. % H0 2

N H Y sample Ε 4

1.06

Number of OH (a) per gram zeolite 7.1 X 10

2(

Δ = 2.5 X N H Y sample F

1.44

9.6 X

10 )

H Y sample

0.69

4.6 X

10

4

G

the

Comparison of Measured and Calculated Measured

Sample

The

10 ' 2

20

20


65.

Moscou

Hydroxyl

343

Groups in Y-Zeolites

p r o p o s e d f o r m a t i o n of a c i d sites b y P l a n k ( 5 ) RE + (H 0) 3

2

> [RE(OH)] + + H+ 2

w h e r e e a c h rare e a r t h i o n f o r m s o n e B r o n s t e d site ( T a b l e I V ) . A t h i g h e r temperatures ( 3 0 0 ° - 4 0 0 ° C ) , d e h y d r o x y l a t i o n o c c u r s ; t h e d i s t i n c t m i n i m u m i n the R E Y c u r v e of F i g u r e 2 indicates that at t h e same Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on December 9, 2014 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0102.ch065

m o m e n t n e w h y d r o x y l s a r e f o r m e d b y another d i s s o c i a t i o n of w a t e r m o l e c u l e s , u p to a m a x i m u m w h i c h has h a l f t h e v a l u e of t h e l o w - t e m p e r a t u r e m a x i m u m . P e r h a p s this c a n b e e x p l a i n e d b y t h e d e h y d r o x y l a t i o n m e c h a n i s m w h e r e 5 0 % of t h e O H g r o u p s lose t h e i r o x y g e n a t o m d u r i n g dehydroxylation a n d consequently cannot be restored b y a n e w l y f o r m e d p r o t o n . It is l i k e l y that t h e increase i n the R E Y c u r v e i n F i g u r e 1 d u r i n g d r y i n g f r o m 5 to 4 % L O I ( w h i c h occurs b e t w e e n 3 0 0 ° a n d 4 0 0 ° C u n d e r t h e c o n d i t i o n s u s e d ) is c a u s e d b y t h e f o r m a t i o n o f O H groups i n t h e β-cage system. T h e o b s e r v e d f o r m a t i o n a n d d e h y d r o x y l a t i o n of B r o n s t e d sites i n R E Y zeolite c a n b e s u m m a r i z e d as f o l l o w s : b e t w e e n 2 0 0 ° a n d 3 0 0 ° C e a c h R E i o n dissociates one w a t e r m o l e c u l e w i t h t h e f o r m a t i o n of o n e B r o n s t e d site i n α-cages, f o l l o w e d b y a d e h y d r o x y l a t i o n b e t w e e n and 400°C.

300°

T h i s is a c c o m p a n i e d b y a n e w d i s s o c i a t i o n of w a t e r m o l e

cules, g i v i n g rise to | B r o n s t e d site i n α-cages f o r e a c h R E i o n a n d to t h e f o r m a t i o n of O H groups i n β-cages. T h i s is i n reasonable agreement w i t h W a r d ' s c o n c l u s i o n that f o r e v e r y 3 exchange sites a m a x i m u m of 2 B r o n s t e d sites are f o r m e d i n R E Y zeolite ( 8 ) .

T h e t h e r m a l s t a b i l i t y c u r v e f o r a c i d i c O H ( a ) groups i n

R E Y zeolites is i n r e m a r k a b l e agreement w i t h its a l k y l a t i o n a c t i v i t y c u r v e as g i v e n b y V e n u t o ( 7 ) . T h e analysis of N H Y zeolites shows that ex 4

c h a n g e of N a b y N H +

4

+

p r i m a r i l y results i n e q u a l amounts of O H groups

i n a- a n d β-cages ( T a b l e V , S a m p l e E ) . E x c h a n g e of t h e m o r e d i f f i c u l t l y e x c h a n g e a b l e N a ions m a i n l y leads H

to inaccessible O H groups i n β-cages

( T a b l e V , Δ b e t w e e n samples Ε

a n d F ) , w h i c h is i n agreement w i t h W a r d ' s conclusions (10).

T h i s agree-

O H ( a ) Densities in N K U Y and H Y Zeolites Calculated % NH in zeolite A

4.02 7.7

Ratio of Measured OH (a) and Total Number of OH

Total number of OH (a) per gram zeolite 14.0 Χ 1 0

20

27.0 X 10* 14.0 Χ 1 0

20

Δ =

13 X 10 ' 2

1 : 2.0 1 : 5.2 1 : 2.7 1 : 3.0


344

M O L E C U L A R SIEVE

ZEOLITES

II

m e n t supports t h e a s s u m p t i o n that O H groups w i t h 3640 c m " i n f r a r e d 1

f r e q u e n c y are the accessible O H groups i n α-cages of t h e zeolite

(6,9,11).

T h e b e h a v i o r o f H Y z e o l i t e resembles c l o s e l y that o f N H Y z e o l i t e ; h o w 4

ever, i t is s u r p r i s i n g that H Y z e o l i t e does n o t s h o w accessible O H g r o u p s after l o w - t e m p e r a t u r e d r y i n g o f t h e samples.


Acknowledgment T h e a u t h o r is g r a t e f u l t o M . L a k e m a n a n d S. L u b f o r excellent as sistance i n t h e e x p e r i m e n t a l w o r k , a n d to P . G . M e n o n f o r m a n y v a l u a b l e c o m m e n t s a n d a d v i c e o n t h e m a n u s c r i p t . T h a n k s are d u e t o J . I. d e J o n g f o r h i s c o n t i n u o u s s t i m u l a t i n g interest i n this w o r k .

Literature Cited (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)

Moscou, L., unpublished results, 1967. Moscou, L., Dutch Patent Application 6713340. Moscou, L., Lakeman, M.,J.Catalysis 1970, 16, 173. Noll, W., Damm, K., Fauss, R., Kolloid-Z.1960,169, 18. Plank, C. J., Proc. Intern. Congr. Catalysis, 3rd, 1965, 1, 727. Uytterhoeven, J. B., Jacobs, P., Makay, K., Schoonheydt, R.,J.Phys. Chem. 1968, 72, 1768. Venuto, P. B., Hamilton, L. Α., Landis, P. S., Wise, J. J.,J.Catalysis 1966, 5, 81. Ward, J. W.,J.Catalysis 1969, 13, 321. Ward, J. W.,J.Phys. Chem. 1969, 73, 2086. Ward, J. W., Hansford, R. C.,J.Catalysis 1969, 13, 364. White, J. L., Jelli, A. N., André, J. M., Fripiat, J. J., Trans. Faraday Soc. 1967, 63, 461.

RECEIVED January 21, 1970.

Discussion J . R a b o ( U n i o n C a r b i d e R e s e a r c h Institute, T a r r y t o w n , Ν. Y . 10591 ) : Y o u r conclusions g e n e r a l l y agree w i t h t h e results w e r e p o r t e d at t h e last I n t e r n a t i o n a l C o n g r e s s o n C a t a l y s i s i n M o s c o w . W h a t rare e a r t h cations d i d y o u use, a n d w h a t w a s t h e total c a t i o n e q u i v a l e n t to a l u m i n u m r a t i o of y o u r catalyst p r e p a r a t i o n s ? L . M o s c o u : W e u s e d a c o m m e r c i a l l y a v a i l a b l e rare earth c h l o r i d e s o l u t i o n i n w h i c h t h e m a i n rare earth elements are l a n t h a n u m a n d c e r i u m . T h e t o t a l c a t i o n e q u i v a l e n t to a l u m i n u m ratio w a s b e t w e e n 1.00 a n d 1.05. D . A . H i c k s o n ( C h e v r o n R e s e a r c h C o . , R i c h m o n d , C a l i f . 9 4 8 0 2 ) : If, as s h o w n i n F i g u r e 2, a c i d i c h y d r o x y l g r o u p s i n a c i d - e x c h a n g e d Y zeolite


65.

Moscou

Hydroxyl

Groups in

345

Y-Zeolites

a p p e a r o n l y o n h e a t i n g above 200 ° C , w h e r e are these groups l o c a t e d i n t h e z e o l i t e structure b e l o w 2 0 0 ° C ? L . Moscou: I n o u r o p i n i o n , the H - Y c u r v e i n F i g u r e 2 i n d i c a t e s that at l o w e r temperatures the a c i d i c h y d r o x y l g r o u p s are l o c a t e d i n β cages a n d that t h e y m o v e i n t o a cages at . — 2 0 0 ° C .

These data support the

c o n c e p t of p r o t o n m o b i l i t y i n zeolites. Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on December 9, 2014 | http://pubs.acs.org Publication Date: June 1, 1971 | doi: 10.1021/ba-1971-0102.ch065

F. W . Kirsch ( S u n O i l C o . , M a r c u s H o o k , P a . 1 9 0 6 1 ) : C a n y o u t e l l m e the size r a n g e of samples u s e d f o r K a r l F i s c h e r a n d l i t h i u m a l u m i n u m h y d r i d e titrations? L . Moscou: T h e size of samples d e p e n d s strongly o n the w a t e r c o n tent a n d thus o n p r e t r e a t m e n t t e m p e r a t u r e of the s a m p l e .

In practice,

it varies b e t w e e n 0.1 a n d 1.0 g r a m . P. Chu

( M o b i l R e s e a r c h & D e v e l o p m e n t C o r p . , P a u l s b o r o , N . J.

0 8 0 6 6 ) : I a m v e r y interested i n the w a y y o u p r e p a r e d the H - Y s a m p l e . W h y d i d w e a k l y a c i d i c o r g a n i c exchange resins h a v e to b e used?

What

degree of exchange c a n y o u a c h i e v e w i t h o u t d a m a g e to the z e o l i t e struc ture? H o w stable t h e r m a l l y is the final H — Y s a m p l e ? L . Moscou: G e n e r a l l y , w e a k l y a c i d i c i o n exchange resins h a v e b e e n u s e d i n o r d e r to p r e v e n t loss of z e o l i t e c r y s t a l l i n i t y . T h i s m e t h o d enables one to exchange at least 7 5 % of the s o d i u m i n Y - t y p e zeolites. s t a b i l i t y of these H - N a - Y zeolites is b e t w e e n 7 0 0 ° a n d 8 0 0 ° C .


Thermal

Acidity, Accessibility, and Stability of Hydroxyl Groups in Y-Zeolites

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